Upgrading SYNC 3.4.20196 to 3.4.21020 taking over 2 hours?

You probably don’t have enough storage (memory) for the install. Follow this tutorial and remove Gracenotes and downgrade to 3.3.19052 (if necessary) to clear up storage space for the update. You don’t need to do the voice file replacement.

Tutorial: Sync 3.4 NON-NAV APIM: Failure to Update to Newer Version Sync 3.4 - Ford / Guides & Info - CyanLabs Official Community